Sorry if this is wrong, I can't seem to find how to post an improvement suggestion here, rather than report a bug.

So Dolphin could use better support for Steam's Overlay. Steam's Big Picture significantly improves emulation with its superb UI for joypad gaming and to be able to use the Overlay with Dolphin games would be great.

I've tried both OpenGL- and D3D11 backends and steam overlay works fine there for me. Though, I don't really care about steam overlay as I run Dolphin windowed but I wanted to give this a shot anyway to see if this issue is invalid or not and it appears to be invalid. Running Dolphin 3.5-1063 x64!

Dolphin 3.5 32-bit works perfectly, 64-bit does not. If I remember correctly Steam did mention in their beta client update that the client does have trouble adding in-game overlays to 64bit non steam games.